This is called the internal Lorentzian angle. (There is a similar formula for exterior Lorentzian angle, see [1]}).
The \(\lbrace 6j\rbrace \) -symbol in this case reads [2]}, [1]}
\(\left\lbrace \begin{array}{ccc}j_1 & j_2 & j_3 \\j_4 & j_5 & j_6\end{array}\right\rbrace \sim \frac{1}{2\sqrt{12\pi |V|}}\cos \phi \exp \left( -\left| \sum _{l=1}^6 \ell _{l} \text{Im}\,\Theta _{l} \right| \right)\,,\nonumber \) 
